The biggest question facing us today in relation to artificial intelligence (AI) is: what if we actually succeed in building superintelligent machines? In particular, what would be the consequences for humankind? This possibility is one of the four ‘existential risks’ that Martin Rees and his colleagues at Cambridge University’s Centre for the Study of Existential Risk are pondering. Such questions go back a long way – at least to 1965, when one of Alan Turing’s colleagues, the mathematician I J Good, observed that ‘the first ultraintelligent machine is the last invention that man need ever make, provided that the machine is docile enough to tell us how to keep it under control’.

That proviso about control provides the spur (and the subtitle) for Stuart Russell’s book. We are currently living through an intellectual feeding frenzy when it comes to AI, stimulated largely by recent advances in machine learning and its widespread utilisation by the technology giants, together with the spectacular